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similar
proprietary software</small><small>.<br>
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            <td colspan="1" rowspan="1" style="vertical-align: top;"> <br>
            <h1 style="text-align: center;"><big><big><big><a
 name="tar_gz_bz"></a>Double, multiple, and hidden file extension<br>
            </big></big></big></h1>
            <br>
            </td>
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 style="vertical-align: top; background-color: rgb(248, 247, 246);"><br>
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 style="background-color: rgb(240, 240, 240); width: 960px; text-align: left;"
 border="0" cellpadding="24" cellspacing="0">
        <tbody>
          <tr>
            <td colspan="1" rowspan="1"
 style="width: 50%; vertical-align: middle; background-color: rgb(255, 255, 255);">
            <div> </div>
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 cellpadding="0" cellspacing="0">
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                  <td style="vertical-align: top;">
                  <ul>
                    <li>
                      <p><a
 href="files-with-double-extension.html#hidden_extension">WHAT ARE
FILES WITH HIDDEN OR
MULTIPLE
EXTENSION</a></p>
                    </li>
                  </ul>
                  <p> </p>
                  </td>
                  <td style="vertical-align: top; width: 128px;">
                  <h2><img title="Multiple file extensions"
 alt="double file extension" src="file-format/security.png"
 style="width: 96px; height: 96px;" align="right"></h2>
                  </td>
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            <td
 style="background-color: rgb(255, 255, 255); vertical-align: top;">
            <div style="text-align: left; color: rgb(0, 0, 0);">
            <h2><big><big><big><a name="hidden_extension"></a><a
 href="files-with-double-extension.html#tar_gz_bz">What are files with
hidden or multiple
extension</a></big></big><br>
            </big></h2>
            </div>
            <br>
            <h3><big>Legitimate use of double file extension</big></h3>
            <br>
PeaZip can handle and create files with double
extension; most common cases for having have a file with two extensions
are<br>
            <table style="width: 100%; text-align: left;" border="0"
 cellpadding="24" cellspacing="0">
              <tbody>
                <tr>
                  <td style="width: 48px; vertical-align: middle;">
                  <h3><img title="Compressed TAR extensions"
 alt="what are TAR.GZ, TAR.BZ, TAR.XZ archives"
 src="file-format/one.png" style="width: 48px; height: 48px;"></h3>
                  </td>
                  <td style="vertical-align: middle;">
                  <h4><span style="font-weight: bold;"></span><big>Compressed
containers</big></h4>
                  <a name="two_extensions"></a>When a
compression only algorithm - most common ones are <a
 href="gzip-utility.html">GZip Deflate compression</a>, <a
 href="brotli-compression-utility.html">Brotli compression</a>, <a
 href="bzip2-utility.html">BZip2 compression</a>, <a
 href="paq-files-compression-utility.html">LPAQ compression</a>, <a
 href="zstandard-compression-utility.html">Zstandard compression</a>
or <a href="7zip-files-utility.html">7-Zip's lzma XZ compression</a> -
is
applied to
multiple files, which consequnetly needs to be
consolidated into a single archive - most times a TAR file -
before the compression step (also known as <a
 href="what-is-solid-compression.html">solid mode compression</a>).<br>
                  <br>
This result in the first step archiving extension (e.g. <a
 href="tar-windows.html">creating a TAR archive file</a>) being
pre-pended to second step compression extension (e.g. XZ).<br>
                  <br>
                  <a name="tar.gz_tar.bz2_extension"></a>Extracting
compressed tar files
(TAR.GZ / TAR.BR / TAR.BZ / TAR.LPAQ, TAR.XZ / TAR.ZST) could be
treated as
atomic,
single step operation, but usually (as in PeaZip, 7-Zip and other
archival utilities) extraction of compressed TAR files is a two step
process which firstly uncompress the TAR archive, and then unarchive
the contained files and folder structure.<br>
                  </td>
                </tr>
                <tr>
                  <td style="width: 48px; vertical-align: middle;">
                  <h2><img title="Split file extensions"
 alt="multiple file extensions" src="file-format/two.png"
 style="width: 48px; height: 48px;"></h2>
                  </td>
                  <td style="vertical-align: middle;">
                  <h4><big>Spanned multi-volume archives</big></h4>
                  <a name="double_extension"></a>File spanning is
applied (often in a single pass) to output archive,
creating a set of volumes of desired size, with a numerator in the file
extension to declare what is the first volume and the progressive order
of data chunks, in example .R01, .Z01, etc<br>
Some splitting standards adds the numerator information in a separate
extension, before or after usual archive extension, in example .7Z.001,
.7Z.002, .7Z.003 etc.<br>
                  </td>
                </tr>
              </tbody>
            </table>
            <br>
            <h3><big>Risks, security issues of "Hide known file
extensions" option</big></h3>
            <br>
A <span style="font-weight: bold;">completely unrelated</span>
use of double file extension spread after Micorsoft set "<span
 style="font-weight: bold;">Hide known
file types extensions</span>" option enabled by default for Windows XP
and
newer systems - this is still the default behavior on Vista, 7, 8, 10 -
opening the ground for attack exploiting hidden files extensions.<br>
            <table style="width: 100%; text-align: left;" border="0"
 cellpadding="24" cellspacing="0">
              <tbody>
                <tr>
                  <td
 style="text-align: right; vertical-align: middle; width: 64px;">
                  <h3><span style="font-weight: bold;"><img
 title="Hide real file type" alt="files with second extension"
 src="file-format/note.png" style="width: 48px; height: 48px;"><br>
                  </span></h3>
                  </td>
                  <td
 style="font-style: italic; vertical-align: middle;">
                  <p><span style="background-color: rgb(255, 238, 221);"><a
 name="hide_real_file_extension"></a></span>This option allows an
attacker to trivially add a file extension before
the true one in order to mask the real nature of the file - being the
last file extension hidden by default to end users by the system in
file browser and most applications following system's file browser
policies.</p>
                  </td>
                </tr>
              </tbody>
            </table>
In example, an executable virus named attachment.exe can be renamed in
attachment.doc.exe.<br>
By deafult, end user would be prompted "attachment.doc" (or any other
harmless file extension used by the attacker, i.e. .jpeg, .mpg), but
once clicked the file would be executed as .exe file (true file
extension) by the system.<br>
In this way an executable file that should trigger a great level of
awareness and caution from user (e.g. .exe, .scr, .bat, .vb, .js...)
can be easily masked as harmless, common, file type to mislead end user.<br>
            <table style="width: 100%; text-align: left;" border="0"
 cellpadding="24" cellspacing="0">
              <tbody>
                <tr>
                  <td
 style="text-align: right; vertical-align: middle; width: 64px;">
                  <h2><span style="font-weight: bold;"><img
 title="Show real file type" alt="hidden file extension"
 src="file-format/information.png" style="width: 48px; height: 48px;"><br>
                  </span></h2>
                  </td>
                  <td
 style="font-style: italic; vertical-align: middle;">
                  <p><span style="background-color: rgb(255, 238, 221);"><a
 name="show_real_file_extension"></a>PeaZip
file and archive browser never hide file extension, avoiding
this type of forgery.</span><br>
Moreover PeaZip warns each time an executable or script file is being
executed from an archive, in this way 1) the user is made aware of the
potentially harmful nature of the file 2) the user can evaluate to
extract the whole archive before, as executable and script
files could need some archived resources (i.e. dll) to be available in
uncompressed form before properly running.</p>
                  </td>
                </tr>
              </tbody>
            </table>
Sometimes files with double extension are treated as suspicious ones,
but if it is the right case for executable ones (exe or script file
type as last extension), it is definitely NOT the case for archive
files with double extension, being TAR.something very common file types
- especially on *x systems.<br>
            <br>
Read more about this topic: <a target="_blank"
 href="https://en.wikipedia.org/wiki/Filename_extension">what are file
extensions<img title="what is filename extension"
 alt="file extension wiki" src="free-rar/extractor.png"
 style="border: 0px solid ; width: 12px; height: 10px;"></a>, list of
known <a target="_blank"
 href="https://en.wikipedia.org/wiki/List_of_file_formats">file
types<img title="file formats wiki list" alt="filename extension"
 src="free-rar/extractor.png"
 style="border: 0px solid ; width: 12px; height: 10px;"></a>, <a
 target="_blank" href="http://www.gnu.org/software/tar/">TAR<img
 title="extract tar.gz files" alt="two file extensions"
 src="free-rar/extractor.png"
 style="border: 0px solid ; width: 12px; height: 10px;"></a> archive
format, which usually comes with a second extension (tar.gz, tar.bz)
declaring the compression scheme applied to the tar container.<br>
            <div style="text-align: left;"> </div>
            <div style="text-align: left;"> </div>
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 style="background-color: rgb(255, 255, 255); vertical-align: top;">
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 style="vertical-align: top; background-color: rgb(72, 136, 248);"><small><span
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                <tr>
                  <td
 style="vertical-align: top; background-color: rgb(240, 239, 238);"><small><a
 href="brotli-compressed-file-format.html">WORK WITH GOOGLE BZ FILE
FORMAT</a><a href="7zip-files-utility.html"> </a></small></td>
                  <td style="vertical-align: top;"><small><br>
                  </small></td>
                  <td
 style="vertical-align: top; background-color: rgb(240, 239, 238);"><small><a
 href="zst-compressed-file-format.html">WORK WITH FACEBOOK ZST FILE
FORMAT</a><a href="7zip-files-utility.html"> </a></small></td>
                </tr>
              </tbody>
            </table>
            <p><a href="peazip-help-faq.html">FAQ</a>
&gt; Security &gt; Files with double extensions</p>
Topics and search suggestions about files with double, second,
multiple, or
hidden extensions, e.g. what are TAR.GZ, TAR.BR, TAR.BZ,
TAR.XZ, TAR.ZST archives; security issues with hidden known file types
extension
and
how to work with file extensions with PeaZip file manager:
            <table style="width: 100%; text-align: left;" border="0"
 cellpadding="6" cellspacing="0">
              <tbody>
                <tr>
                  <td
 style="vertical-align: top; width: 25%; font-style: italic;">what are
files with double extension, <br>
hide file
extension, <br>
spanned archives 7z.001,<br>
files with two extensions,<br>
hide ral file extension,<br>
what are TAR.BZ archives<br>
                  </td>
                  <td
 style="vertical-align: top; width: 25%; font-style: italic;">split
zip.001 files, <br>
hide real file type, <br>
what are TAR.ZST files,<br>
tar.gz extension, <br>
tar.bz file type,<br>
hidden real file extension,<br>
                  </td>
                  <td
 style="vertical-align: top; width: 25%; font-style: italic;">why
multiple file extensions, <br>
meaning of double file extension, <br>
hidden file extension security risk,<br>
unhide file extension,<br>
what are TAR.BZ archives<br>
how to display real file type<br>
                  </td>
                  <td
 style="vertical-align: top; width: 25%; font-style: italic;">second
file extension, <br>
two file extensions, <br>
show real file type,<br>
what are TAR.XZ archives<br>
display real file extension,<br>
show real file extension<br>
                  </td>
                </tr>
              </tbody>
            </table>
            </td>
          </tr>
        </tbody>
      </table>
      <table
 style="background-color: rgb(255, 255, 255); margin-left: auto; margin-right: auto; width: 960px; text-align: left;"
 border="0" cellpadding="24" cellspacing="0">
        <tbody>
          <tr>
            <td style="vertical-align: top;">Tag Cloud<br>
            <span class="wrd free-rar2"
 id="compressed-tar-double-extension"> <a
 href="files-with-double-extension.html">TAR.GZ / .BZ double extension</a></span>
            <span class="wrd free-rar3"
 id="spanned-zip-double-file-extension"> <a
 href="files-with-double-extension.html">ZIP.001 double file extension</a></span>
            <span class="wrd free-rar1"
 id="antivirus-scan-inside-rar-zip-archives"> <a
 href="antivirus-scan-zipped-files.html">antivirus scan inside rar zip
archives</a></span> <span class="wrd free-rar2"
 id="change-file-password"> <a href="change-password.html">change
password of file</a></span><br>
            <span class="wrd free-rar1" id="find-duplicate-files"> <a
 href="duplicates-hash-checksum.html">find
duplicate files</a></span> <span class="wrd free-rar2"
 id="hide-filenames-in-archives"> <a href="encrypt-filenames.html">hide
filenames in archives</a></span> <span class="wrd free-rar4"
 id="files-with-double-extension"> <a
 href="files-with-double-extension.html">files with
double extension</a></span> <span class="wrd free-rar0"
 id="use-multiple-encryption-passwords"> <a
 href="multiple-passwords.html">files with multiple encryption passwords</a></span>
            <span class="wrd free-rar2" id="recover-password"> <a
 href="peazip-password.html">recover password</a></span> <br>
            <span class="wrd free-rar3" id="protect-files"> <a
 href="protect-files.html">protect
files</a></span> <span class="wrd free-rar2"
 id="quantum-computing-cryptography"> <a
 href="quantum-computing-cryptography.html">quantum computing
cryptography</a></span> <span class="wrd free-rar1"
 id="safely-share-files"> <a href="share-files-sharing.html">safely
share files</a></span> <span class="wrd free-rar0"
 id="file-hashing-checksum-tools"> <a href="verify-checksum-hash.html">checksum
hash tool</a></span> <span class="wrd free-rar1"
 id="free-rar-zip-files-conversion-utility"> <a
 href="convert-files.html">free
RAR ZIP files conversion utility</a></span> <span class="wrd free-rar3"
 id="file-compression-archiving-application"> <a href="index.html">free
file archiver</a></span> <br>
            <span class="wrd free-rar1" id="free-ace-files-opener"> <a
 href="ace-files-utility.html">free ACE
opener</a></span> <span class="wrd free-rar0"
 id="manage-microsoft-cab-files"> <a href="cab-files-utility.html">manage
CAB files</a></span> <span class="wrd free-rar2"
 id="encrypted-files-extraction-utility"> <a
 href="extract-encrypted-files.html">encrypted
files extraction utility</a></span> <span class="wrd free-rar1"
 id="how-to-extract-archives"> <a
 href="how-to-extract-rar-zip-archives.html">extract RAR TAR ZIP files</a></span>
            <span class="wrd free-rar4" id="download-free-rar-software">
            <a href="index.html">free RAR download</a></span> <span
 class="wrd free-rar1" id="bz2-file-extension"> <a
 href="bzip2-file.html">.BZ2 file extension</a></span> <br>
            <span class="wrd free-rar1" id="split-file-spanning-how-to">
            <a href="file-split.html">how to
split files</a></span> <span class="wrd free-rar2"
 id="work-with-7z-7zip-files"> <a href="7zip-files-utility.html">work
with 7Z archives</a></span> <span class="wrd free-rar4"
 id="free-rar-files-extractor"> <a href="free-rar.html">free RAR
extractor</a></span> <span class="wrd free-rar3"
 id="free-zip-files-opener"> <a href="zip-files-utility.html">free ZIP
files opener</a></span> <span class="wrd free-rar0"
 id="portable-rar-files-software"> <a href="peazip-portable.html">portable
RAR TAR ZIP software</a></span> <span class="wrd free-rar2"
 id="what-are-rar-files"> <a href="what-is-rar-file.html">.RAR
files</a></span><br>
            <span class="wrd free-rar1" id="secure-delete-data"> <a
 href="secure-delete.html">secure
delete data</a></span> <span class="wrd free-rar3"
 id="free-tar-utility-for-windows"> <a href="tar-windows.html">Windows
TAR files utility</a></span> <span class="wrd free-rar2"
 id="what-is-zip-file-type"> <a href="zip-file-format.html">ZIP file
format</a></span> <span class="wrd free-rar1"
 id="free-rar-tar-zip-files-utility"> <a href="index.html">free rar
tar zip utility</a></span> <span class="wrd free-rar0"
 id="free-zipx-utility"> <a href="zipx-files-software.html">free ZIPX
utility</a></span> <span class="wrd free-rar4"
 id="what-is-gz-file-format"> <a href="gzip-files.html">.GZ files</a></span>
            <span class="wrd free-rar0"
 id="open-source-encryption-software"> <a href="encrypt-files.html">open
source encryption tool</a></span> <br>
            <span class="wrd free-rar3" id="what-is-gz-file-format"> <a
 href="gzip-utility.html">free GZ files utility</a></span> <span
 class="wrd free-rar2" id="what-is-gz-file-format"> <a
 href="bzip2-utility.html">BZip file compression tool</a></span><br>
            </td>
          </tr>
        </tbody>
      </table>
      <br>
      </td>
    </tr>
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      <td
 style="vertical-align: top; background-color: rgb(243, 242, 241);">
      <table
 style="margin-left: auto; margin-right: auto; width: 960px; text-align: left;"
 border="0" cellpadding="0" cellspacing="0">
        <tbody>
          <tr>
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            </td>
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            </td>
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          <tr>
            <td style="vertical-align: top; width: 25%;"><small> <img
 alt="spanned file extension" src="titles.png"
 style="width: 129px; height: 2px;"><br>
            <a name="multiple_file_extensions"></a>DOWNLOADS<br>
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 src="free-rar/extract-rar.png" style="width: 1px; height: 1px;"
 vspace="3"><br>
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 alt="split file extension" src="titles.png"
 style="width: 129px; height: 2px;"><br>
            <a name="hidden_file_extension"></a>SUPPORT<br>
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 style="width: 1px; height: 1px;" vspace="3"><br>
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help</a><br>
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Asked Questions</a><br>
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information</a></small><br>
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 alt=".r01 .r02 .r03" src="titles.png"
 style="width: 129px; height: 2px;"><br>
            <a style="color: rgb(0, 0, 0);"
 name="spanned_file_extension"></a>DONATE<br style="font-style: italic;">
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 style="width: 1px; height: 1px;" vspace="3"><br
 style="font-style: italic;">
Support
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project,
or donate to FAO,
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                  <td style="text-align: right; vertical-align: middle;"><small><a
 target="_blank"
 href="https://github.com/giorgiotani/PeaZip/releases.atom">Releases
Feed</a></small></td>
                  <td
 style="text-align: right; width: 30px; vertical-align: middle;"><small><img
 alt="what are of TAR.GZ, TAR.BZ, TAR.XZ files"
 title="PeaZip releases feed" src="extract-zip/rss16.png"
 style="width: 24px; height: 24px;" align="middle"></small></td>
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 target="_blank" href="https://github.com/giorgiotani/PeaZip/wiki">PeaZip
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 href="mailto:giorgio.tani.software@gmail.com">Developer email</a></small></td>
                  <td
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 alt="Files with double extensions"
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 style="width: 24px; height: 24px;"><br>
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                  </small></td>
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 style="text-align: right; width: 30px; vertical-align: middle;"><small><img
 alt="multiple file extensions" title="Search in PeaZip project domain"
 src="extract-rar/rar-opener.png"
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